US2592522A - Dynamoelectric machine and control - Google Patents

Description

Ap 8, 1952 M. HENDRICK ET'AL DYNAMQiiEECTRIC MACHINE :AND CONTROL 3 SheetS-Sheet 1 Filed Jan. 12, 1950 y Their Attor hey.

April 8, 1952 M. HEN-DRICK ETAL DYNAMOEIJECTRIC MACHINE AND CONTROL 3 Sheets-Sheet 2 Filed Jan. 12 1950 w n A m4m u 0404 a m E N H m R w "N |1 |||L lllll.

4 2 4 4 w o W 2 L l w I 3 F 4 4 v R I v H w E L B A C D m L f Inventor: Lloyd M. Hendrick, Charles MWheeler,

Their" Attorney April 8, 1952 I L, M. HENDRICK ETAL 2,592,522

DYNAMQELEC TRIC MACHINE AND CONTR6L 7 Filed Jan. 12 1950 3 Sheets-Sheet :5

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TERMINAL VOLTS LINE ANPERES AHPERES 20 SECONDS Inventor-s: Lloyd M. Hendrick, Char-[es M. Wheeler,

Their Attorney.

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It anobject of the present invention to. pro- Patented Apr. 8,

. D -.STAT.ES -PATENT OFFICE DYNAMOELECTRIC MACHINE AND CONTROL Lloyd 7 M. Hendrick and ,Charles M. Wheeler, Fitchburg, Mass., assignors to General Electric Company, a corporation of New York Application January 12,1950, Serial No..138, 152 7 Claims. ((31 322 -53) Ourinvention relates toelectrical equipment and control and more particularly to generators tusadaptedto supply electrical energy to lightwei ht' equipment such as an aircraft engine 'startermotor.

Ithas previously been known to supply a constant current power. Supply characteristic for "starting jet or other type aircraft engines, with the consequent advantage of 'a high ratio of starter motoipower to starter motor weight.

The necessary thermal capacity or size ofa motor is .dependent upon current values during the f Starting'cycle, and the size -of' current carrying elements (including brushes andcommutator, if 'fany'),.of 'a motor are also dependent primarily "upon the peak value of current obtained dur- .mg the starting cycle. Therefore, from the f f standpoint of motor weight alone, it is doubly ben'efioial to eliminate the current peaks. which 'wwoiild be causedduring the starting cycle if a motor were to be' placed across a constant voltage source or if ordinary time, or current respon- Ysive'starting control were used. Furthermore, the weight of the mechanical connection between any motor and the device it drives, is determined largely by shocks aptto be encountered during starting and if suchshocks can be modified by 'eli minating high peaks of current (i. e., torque),

the equipment. may bemade lighter which is of special importance if the motor and its driving connection are tobe airborne. Heretofore, it has been known to supply constant current by the use of acurrent regulator together with the use of a separate exciter machine but such means are costly andintroduce complicated maintenance problems. It has also been previously known to 1'. start agenerator from zero voltage by the use of 'jarmatu're', short circuiting contacts, but this is likewise expensive and often causes excessive and even destructive heating in the generatorand in vide sn'npieand inexpensive means for overcoming' the above-mentioned difficulties.

A further object of the presentv invention is to provide a self-excited dynamoelectric machine affording zero to constant current regulation.

Astill further object of theinvention is to procreasing power, third, power having a constant current characteristic, fourth, power having a constant, voltage characteristic, fifth, zero power after a predetermined low current cut off.

Another object of the present invention is to provide a novel combination of constant current generator. and control'therefor to make the same useful as a non-airborne aircraft energizer, al-

though the same generator-control combination may have other uses such as to supply constant current for battery charging.

Broadly, the means employed in the embodiments herein illustrated and described comprise a generator of split poledesign and having a mainfieldexciting winding and a cross or regulating'field exciting winding together with controlmeans for starting at zero voltage by having the cross field reversed with respect to the main fieldand thereafter transposing the cross field to allow a voltage builtup until an inherent constant current characteristic of the machine is reached, thereby to eliminateheavy inrush currents to. the electric device thereby supplied and also minimize strains and shocks on mechanical partsas'sociated with such device.

other objects and advantages will become apparent and our invention will be better understoo'dfby consideration of the following descrip- ,tion taken in connection with the accompanying 'drawingmin which Fig. lrepresents a simplified schematic diagram of a power system including a jet aircraft engine, an airborne electric starter motor therefor, and a ground based power sup- ,fply for, the starter with said supply comprising.

analternating current motor, a D.-C. generator and certain hereinafter described control for the 1 generator; Fig. 2 is a simplified connection diagram forthe generator shown in Fig. 1 but with a modification in the control thereof; Fig. 3 is ayolt ampere characteristic curve for a system Q of the type shown in Figs. 1 and 2; and Fig. i iis a typical time current characteristic for the same system.

"Referring now to Fig. 1, III is an aircraft jet engine adapted to be driven by a 11-0. starter motor'having' an 'armature II and a series field winding l2. Beca us e,of the tremendous rotational inertia of an engine of the jet type, the starter motor (lll2) is of necessity of rather large size (for example H. P.). In order to reduce weight on the aircraft, such large starter motors are customarily energized from a ground (or aircraft carrier borne) power supply and in the illustrated embodiment this power supply comprises l Di-Cg generator ,l 3 adapted to be driven by an A. C. motor |4, although, if desired, the generator may be driven by any convenient source of mechanical power such as an automobile type engine. The generator l3 (shown in Figs. 1 and 2) is a modification of the split pole type generator described and claimed in U. 8..

Patent 1,340,004, issued May 11, 1920 on an application filed by Sven R. Bergman, and assigned to the assignee of the present invention. In accordance with the teachings of the patent, the generator is provided with an armature and a commutator diagrammatically represented by the circle l5, and the commutator is contacted by load brushes l6 and H and an auxiliary or third brush 18. As shown in Fig. 2, the field magnet structure has two sets of field poles l9 and 2|. As explained in the Bergman patent one of said sets of poles (I9) is arranged to be substantially saturated (so that the flux in said set is practically unaffected by armature reaction when the set is excited by current in a shunt field exciting winding 20 wound thereon and connected between the auxiliary brush l8 and load brush l6) The poles l9 may be referred to as the main poles and if desired, the saturation may be achieved by cutting saturating notches I911, (Fig. 2) in these poles. The poles 2| of the other set may be referred to as the cross poles. In the Bergman patent the cross poles are arranged to operate unsaturated (so as to be affected by armature reaction). In the present invention the cross poles 2| are provided with a shunt field exciting winding 22 connected through means (such as a three pole double throw switch 23 as in Fig. 1

or a relay 23a as in Fig. 2) for selectively connecting the winding across brushes l6 and I8 or across load brushes I and I1. During operation, main poles H) are saturated and the flux therein will not vary with load and the voltage across brushes I6 and I8 will remain constant. However, the cross poles 2| having the flux varied by current in winding 22 (dependent on terminal volts for one positionof the reversing device) are unsaturated to the extent that the total flux through these poles is (for this position of the reversing device) by predetermined design caused to reverse at a specific value of load current due to the effect of armature reaction being greater than the flux caused by winding 22 at this specific value of load current. The winding 22 is so connected that when the switch 23 (of Fig. 1) is in position A, the voltage produced between brushes I1 and I8 (from winding 22) opposes the voltage between brushes l8 and I6 (from winding 20) and the output voltage of the machine will be zero since the load voltage is equal to the algebraic sum of the two voltages, one across brushes l6 and H3 and the other across brushes l1 and I8, and with switch 23 in position A these two voltages are (with proper design or the machine) equal and opposite. When the switch 2| is subsequently thrown to position B the field winding 22 is connected across brushes I6 and II in such direction that it opposes the armature reaction component effective in its own axis, so that the flux in the associated poles (2| or Fig. 2) tends to be varied by the armature reaction and the voltage between brushes and I8 (and consequently the voltage across the load brushes l6 and I8) decreases when the load current increases.

If desired, in order to obtain desirable commutation, a commutating pole windin 24 may be connected in series with the armature as shown.

The main field winding 20 is permanently connected across one main brush and the auxiliary brush and the switching means indicated generally at 23 (or 23a.) are provided so that the cross field winding 22 may be first connected across the same main brush and auxiliary brush l8 of the generator to obtain zero voltage due to the opposing effects of the fields. This allows the cross field to be reconnected for a soft start (as hereinafter explained) as it is subsequently connected across the same main brush and the other main brush of the generator to eventually obtain constant current regulation. If desired, additional advantageous results may be secured if a voltage regulator indicated generally at 25 is included in the cross field circuit to regulate the generator output voltage to a maximum preset value (such as 28%; volts) without disadvantageously affecting constant current regulation. Regulator 25 may be of the conventional carbon pile type having a carbon pile resistance element 28 adapted to be compressed or decompressed by a solenoid coil 21 arranged in series with an adjusting rheostat 29. Coil 21 and rheostat 28 are placed across the load brushes to be responsive to the output of the machine, and the carbon pile 26 is placed in series with the cross or regulating field winding 22 and the combination has an amplifying effect inasmuch as the regulating excitation need be only a small fraction of the total excitation of the split pole generator.

In order to prevent the motor II from feeding back into the generator, an automatic cutout or reverse current relay 29 is provided and in the illustrated embodiments of Figs. 1 and 2, this relay serves the added purpose of acting as a line contactor in the generator output or loop circuit between motor and generator. Relay 29 is of conventional type having a main contact 30, a reverse current series coil 3|, a voltage relay coil 32 (to prevent the main contact being closed before the generator has been brought up to speed), a differential voltage coil 33 (to prevent the main contacts closing except with proper polarity), voltage relay contact 34 (closed when coil 32 is energized) arranged in series with coil 33 across the initially open main contacts 30. The series coil 3| and difierential voltage coil 33 are arranged on the core of a relay having a normally open contact 35 which when closed energizes the main contactor coil 36 closing contacts 30 to connect the generator to its load. There is also a starter switch 31 (which may conveniently be located on the aircraft itself so that the pilot will have some control of the starting cycle). As shown in Fig. 1, the relay 29 is adapted to be energized to close line contact 30 as soon as switch 23 is thrown to the B position whenever starter switch 31 is closed.

Further advantageous results may be obtained by the use of high voltage low current cut-off control such as that shown in Fig. 2. In Fig. 2, the startin is remotely controlled since the reversing relay 23a has a coil 38 adapted to be energized as by a battery 39 when the pilots switch 31 is closed to energize reverse current relay 29. However, as illustrated in Fig. 2, the circuit to relay 29 must be completed either through a normally closed contact 4| on a high voltage relay HVR or through a normally open contact 42 on a low current relay LCR. High voltage relay HVR has a coil 43 connected to be responsive to output voltage as by being connected across the generator output brushes, and low current relay LCR. has a coil 44 which is connected to be responsive to output current as by being connected across the commutating field to be responsive, voltage drop thereacroiss.

The characteristics of the arrangement described are shown in Figs. Band 4'; Fig. 3 illustrates generator output characteristic'with a load assumed by way of example 'to'be'an' aircrait jet engine direct coupled starter. When a age (soft start) sequence is initiated," current and voltage build up'ra'pidly from origin 5!) along a resistance line 5] (dependent up Q'n stalled niotorand lead resistance) to ap'oint 52 at or near which point the starter 'motor' commences to crank. The starter accelerates the engine at constant current along a line" 53 and after the engine fires and begins to'furnish some torque itself current is reduced to a point 5 4,"where the voltage regulator is able to take controlso that the characteristic follows a constant voltage line 55. At a'point .SF'thecurrntis cut fofieither manually or by some automatic means (such as by the HVR, LCR and reverse current relay cornbination shown in Fig. 2' and further described hereinafter in connection with Fig. 4). Beyond this point 55 the jet engine has enough torque to sustain itself.

Fig. 4 illustrates a soft start characteristic 51 of an energizer basedion actual field tests (in normal winter conditions in northern United States) upon an airplane having a large jet engine. 'Although current input'to the starter motor rises rapidly during the first second, the in- .ofi point 5.9, the energizer isdisconnected'from the starter motor by means such as that indicated diagrammaticallyin Fig. 2, as contact 42 of LCR which at low current opens and interrupts voltagev supplied to coils 32 and 36 (relay 2!!) since HVR is energized. During the initial starting cycle, however, thevoltage output of the generator islow so that H VR is dropped out (contact 4| closed) andthe low current relay has no efiect upon the control.

In operation, when the pilot closes his starting switch 31, the following sequence is initiated? 1 FR relay 23a. coil38is energized and reconnects the cross field-allowing the armature voltage to build up from the substantially zero voltage previously caused, as hereinabove explained, and, at the sametime, there'verse. current relay 29 becomes energized. and its main contacts 3d close connecting the. generatoruto .the starter motor.

2.-The current will .then increase along the resistance line 5| (Fig. 3) .totherpoint. 52, but before point 52 isreached LCR relaycoil 44 .(Fig. 2) becomes energized.

3. Thereafter, l-IVR relay coil vA3 (which is connected across the output brushes) becornes energiz-ed opening contact 4!.

4. When vthe .loop. circuit current decreases (due to back E. M. F.,of the starting motor) to a predetermined value, LCR becomes dc-energized and disconnects the energizer. from the starting motor.

5. When the switch 31 .is subseguentlyopened or when .theload cable leads are disconnected from the aircraft, .F'Rrelaycoilj'fl is. de enen ,6 gized allowing the cross-field to reverse and bring the generator voltage *back'to zero m readiness. tor the'next start.

"With the'arrangement as above described, the.

generator supplies both regulated voltage with. variable current and approximately constant current with variable voltage with the latter characteristic controlled'inherently by the gen-- erator design. Insofar as aircraft engine starting is concerned, this permits avoiding high peaks of starting current" (such as those caused when constant or adjustable sources'of voltage areused) "and consequent overheating of the starter motor and shocks on the mechanical connections between the starter and the jet engine. Thus, withthe invention the starting motor and its connections wi'th'the engine may be made smaller and'the payload of the aircraft may be made larger. 1

While we have illustrated and described particular embodiments of our invention, modifications thereof will occur to those skilled in the art. We desire it to be understood, therefore, that our invention is not to be limited to the particular arrangements disclosed, and we intend in the appended claims to cover all modifications which do'not depart from the spirit and scope of our invention.

What we claim as new and desire to secure by Letters Patent of the United States is:

l. Cur1'ent supply means for a load comprising in combination a direct current generator having two 'load'brushes and an auxiliary brush located therebetween and having two field exciting windings, means including connections for selectively first energizing said field exciting windings diiferentially from one of saidload brushes 'andsaid auxiliarybrush so that the net voltag'eoutput across 'said'load brushes is substantially zero and secondly energizing one of said field exciting windings from one of said load brushes and said auxiliary brush and the other of said fieldexciting windings from said'load brushes so thatthe energization of'said second winding will be initially zero for said second cohdit'ion and the "voltage output 'at' said load brushes may gradually build up from said zero value 'as' determined by the excitation of said windings and the effect of armature reaction.

2. Current supply means comprising. in combinationa direct current generator having two field exciting windings, control means for first energizing said field exciting windings so that the net voltage output of said generator is substantially zero, control means for secondly energizing one of said field exciting windings from said net voltage output so that for said second condition the field excitation will initially be only that produced by the other of said field exciting windings. 3; A dynarnoelectric machine haing an armature provided with a commutator,- load. brushes and an auxiliarly brush bearing on said commutator, a field magnetic structiue having two sets of field poles,'field exciting windings on said poles with the poles and windings arranged so that one of said sets of poles is substantially saturated'so that the flux in said set is unaffected hy armature reaction and produces a constant voltage between said auxiliary brush and one of said load brushes and the other of said sets is substantially unsaturated so that the fiux therein is du'ced by'said 'set and consequently the voltage across the lioad brushes decreases at a sharp rate 7.5" when the load currentincreases beyond a predewaste second across said load brushes to set up flux in said unsaturated poles in the proper direction to oppose the component therein f fiux produced by armature reaction.

4. A dynamoelectric machine having an n pole armature winding, a field structure comprising 2 n mechanical field pole pieces arranged in two sets with an equal number of pole pieces in each set, means for providing a substantially magnetically saturated path in the magnetic circuit of one of said sets of pole pieces so that the flux in said set is substantially unaffected by armature reaction, the magnetic circuit of the other of said sets of pole pieces and the electrical circuits associated therewith being arranged so that the flux therein may be substantially varied by armature reaction, load brushes and an auxiliary brush co-operating with said armature winding, said load brushes being arranged with respect to said pole pieces so that the voltage difference between said brushes is dependent on the flux in both of said sets of pole pieces, said auxiliary brush being arranged with respect to said pole pieces so that the voltage between said auxiliary brush and one of said load brushes is dependent on the flux in said magnetically saturated set of pole pieces with a consequent constant voltage across said brushes, a shunt field exciting winding on said saturated set of pole pieces connected across said brushes having constant voltage thereacross, a shunt field exciting winding on said unsaturated set of pole pieces, a reversing device connected to said last mentioned exciting winding, connections from said reversing device to said brushes having constant voltage thereacross to allow said last mentioned winding to produce a voltage across said auxiliary brush and the corresponding one of said load brushes equal to but opposing said constant voltage, and connections from said reversing device to both of said load brushes to allow said last mentioned winding to produce a fiux opposing the armature reaction component in the same axis, thereby to selectively allow zero output and desired current output from said dynamoelectric machine to provide a soft start to any apparatus adapted to be supplied therefrom.

5. A generator having a n pole armature winding, a field structure comprising 2 n mechanical field pole pieces having windings and arranged in two sets with an equal number of pole pieces in each set, means for providing a substantially magnetically saturated path in the magnetic circuit of one of said sets of pole pieces so that the flux in said set is substantially unafifected by armature reaction, the magnetic circuit of the other of said sets of pole pieces and the electrical circuits of windings thereon being arranged to operate unsaturated so that the flux therein may be substantially varied by armature reaction, load brushes and an auxiliary brush co-operating with said armature winding, said load brushes being arranged with respect to said pole pieces so that the voltage difierence between said brushes is dependent on the flux in both of said sets of pole pieces, said auxiliary brush being arranged with respect to said pole pieces so that the voltage between said auxiliary brush and one of said load brushes is dependent on the flux in said magnetically saturated set of pole pieces with a consequent constant voltage across said brushes, said pole piece windings including a shunt field exciting winding on said saturated set of pole pieces connected across said brushes having constant voltage thereacross, a shunt field excitin Winding on said unsaturated set of pole pieces, a

reversing relay having positionable contacts, connections from said last mentioned field exciting winding through said contacts in one position thereof to said brushes having constant voltage thereacross to allow said last mentioned winding to produce a voltage across said auxiliary brush and the other of said load brushes equal to but opposing said constant voltage, connection from said last mentioned winding through said contacts in another position thereof to both of said load brushes to allow said last mentioned winding to produce a flux opposing the armature reaction component in the same axis, a voltage regulator having its operating element connected across the output of said generator and its regulated element interposed between said last mentioned existing winding and said reversing relay contacts, an operating coil for said reversing relay, means including a source of control power and circuit making means in series circuit therewith for energizing said reversing relay coil, said circuit making means including a second relay having a contact closed when said second relay is deenergized and including a third relay in parallel circuit having a contact open when said third relay is deenergized, connections for energizing the operating element of said second relay in response to a predetermined high voltage across the output of said generator, connections for energizing the operating element of said third relay in response to a predetermined high current value in the output circuit of said generator and connections placing said second and third relay contacts in parallel with each other and in series with said circuit making means in series with said source of control power and said reversing relay coil.

6. Apparatus adapted to supply electrical energy to a load comprising electrical equipment having a high ratio of power to Weight, said apparatus including a D. C. generator, means for driving said generator, and electrical control, said generator being a split-pole generator of the constant current type having load brushes and a third brush and adapted to be operated with saturated main poles and unsaturated cross poles and having a Winding on said cross poles, and said electrical control including means for first energizing said cross pole winding first from one load brush and said third brush to provide zero output from said machine and secondly from said load brushes to provide a soft start before the constant current output characteristic of said machine is reached.

'7. Apparatus adapted to supply electrical energy to a load comprising electrical equipment having a high ratio of power to weight, said apparatus including a D. C. generator, means for driving said generator and electrical control, said generator being a split pole generator of the constant current type having two load brushes and a third brush and adapted to be operated with saturated main poles and unsaturated cross poles and having a winding on said cross poles, said electrical control including means for first en- 9 ergizing said cross pole winding first from one load brush and said third brush to provide zero output from said machine and secondly from said load brushes to provide a soft start before the constant current output from said machine is reached, said control including a voltage regulator arranged responsive to voltage across said load brushes and connected to vary the cross field winding energization above a predetermined high voltage value, and said control including relay means arranged to connect said apparatus first with said zero output to said load responsive to supervisory control, and finally to disconnect said apparatus from said load and simultaneously again arrange to energize said cross pole winding for zero output upon the simultaneous occurrence of said high voltage value and a predetermined low value of current through said load.

LLOYD M. HENDRICK. CHARLES M. WHEELER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date Beetem July 12, 1932 Burnham Aug. 15, 1911 Bergman May 11, 1920 Bergman May 11, 1920 Steel: Aug. 22, 1922 Perkins Mar. 30, 1926 Hillebrand Feb. 11, 1928

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